Recently, a demand for fuel efficiency in automobiles has been increased, and as a material for tires for automobiles, particularly a material for a tire tread contacting the ground, development of a material having a low rolling resistance has been demanded. On the other hand, from the viewpoint of safety, a material having a high wet skid resistance, and practically sufficient abrasion resistance and breaking properties has been demanded.
Conventionally, as a reinforcing filler for the tire tread, carbon black, silica, and the like have been used. Use of silica has an advantage in the hysteresis loss reduction and the wet skid resistance improvement. However, contrary to carbon black having a hydrophobic surface, silica having a hydrophilic surface has disadvantages such as small affinity with a conjugated diene rubber and dispersibility inferior to that of carbon black. For this reason, a silane coupling agent and the like need to be additionally contained in order to improve dispersibility and bond silica to the rubber.
Further, recently, by introducing a functional group having affinity or reactivity with silica into a chain end of a rubber molecule having high mobility, attempts have been made to improve dispersibility of the silica in a rubber composition, to reduce the mobility of the chain end of the rubber molecule, and further to reduce hysteresis loss.
For example, Patent Document 1 proposes a modified diene rubber obtained by reacting a modifier having a glycidyl amino group with an active polymer end. Patent Documents 2 to 4 propose modified diene rubbers obtained by reacting alkoxysilanes containing an amino group with an active polymer end, and compositions of these modified diene rubbers and silica. Patent Document 5 proposes a polymer functionalized by reacting a cyclic azasilane compound with an active polymer end. Patent Document 6 proposes a diene rubber obtained by a coupling reaction of an active polymer end with a polyfunctional silane compound.